This investigation is interested in exploring how a single essential amino acid, specifically L-tryptophan, affects protein metabolism in the liver. In earlier reports from our laboratory we have described that L-tryptophan rapidly stimulates hepatic polyribosomal aggregation and protein synthesis. This effect appears to be related to alterations in both transcriptional and postranscriptional controls. Our present proposal plans to explore at the cellular and subcellular levels how L-tryptophan may act, possibly directly on the nucleus (nuclear membrane), to stimulate enhanced nucleocytoplasmic translocation of mRNA. We plan to study in detail how proteins of the cytosol and nuclear membranes of the livers of tryptophan-treated rats are involved in the increased nucleocytoplasmic translocation of mRNA. Also, we plan to investigate how tryptophan acts in improving hepatic protein synthesis in rats treated with hepatotoxic agents. Such information may offer basic insight as to how an important dietary component, as exemplified by L-tryptophan, may plan a regulatory role in mammalian liver protein metabolism.